A new study finds that rates of serious child abuse have risen slightly in the U.S. over the past 12 years, suggesting that other data showing a decline in abuse may be due to differences in reporting, rather than a true reduction in abuse-related injuries.

Reporting in the journal Pediatrics, researchers from the Yale School of Medicine examined trends in serious injuries from child abuse from 1997 to 2009 using the Kids’ Inpatient Database (KID) — a sample of youth hospital discharges in the U.S. The researchers defined serious injuries as head injuries, fractures, burns, open wounds and abdominal injuries.

Over the 12-year period studied, the researchers found that serious injuries increased by about 5% overall, rising from 6.1 injuries per 100,000 children ages 18 and younger in 1997 to 6.4 in 2009. Serious injuries increased most in the youngest children — those under age 1 — by 10.9%.

The new findings counter data from child protective services, which show a 55% decrease in physical abuse from 1992 to 2009. One possible explanation for the discrepancy is that protective services accounts for all physical abuse in their calculations — regardless of severity or age — whereas the authors of the current study looked specifically at severe injuries requiring hospitalization.

They also noted that most such severe injuries affect babies under 1, so even if all physical abuse is declining in the U.S., harm to very young children hasn’t been following the same trend line. In fact, the new study showed that older children actually saw a decrease of serious injury, by 9.1%, from 3.3 to 3.0 injuries per 100,000 children over the 12-year study period.

The authors also note that serious abuse-related injury increased among children on Medicaid, from 59% to 74%. “That three-quarters of the abused children in 2009 were on Medicaid highlights the importance of poverty as a stressor for families and suggests that funding from Medicaid might target the prevention of these serious injuries,” the authors write.

Ultimately, the study shows that child abuse rates can’t be reliably tracked using just one source of data, the authors said. Further, efforts to protect children at home, in day care or in other caregiving situations need to be ramped up. “These results highlight the challenges of helping parents do better by their children and the importance of effective prevention programs to reduce serious abusive injuries in young children,” study author Dr. John M. Leventhal, professor of pediatrics and nursing at Yale, and director of the Child Abuse Programs at Yale-New Haven Children’s Hospital, said in a statement.

As Leventhal told HealthDay, he often advises frustrated parents to “take five”: “Step back, take a deep breath and walk out of the room.” He also cautioned that children are often hurt by people outside their family: “Be careful about whom you leave your kids with, and even if it is embarrassing, say ‘Don’t hurt my kid when you take care of them,'” he told HealthDay.